Method for forming carbonaceous hard films

ABSTRACT

A method for enabling the formation of a carbonaceous hard film having a high hardness, strong adherence to the substrate, a wide range of substrate compatibility, and structural stability, which can be formed at room temperature and may cover a large area. The method includes vapor depositing a hard film of a carbonaceous material onto a substrate under vacuum by depositing a vaporized, hydrogen free carbonaceous material, which may be ionized or non-ionized, onto the substrate surface while irradiating the carbonaceous material with gas cluster ions, generated by ionizing gas clusters to form the film.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of U.S. application Ser. No.09/443,995 entitled “Method for Forming Carbonaceous Hard Film”, filedNov. 19, 1999, such application being incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The invention is directed to a method and apparatus for forming acarbonaceous hard film and a device therefor. In particular, theinvention is directed to a method and apparatus for forming a novelcarbonaceous hard film having a dramatic surface-improving effect, whichis useful in tools and moving parts where a high hardness, wearresistance, and reduced friction are required, and in precisionelectronic instrument parts and the like.

[0003] In recent years, higher hardness and higher functionality arebeing required more and more from hard coatings for industrial use. Inthese circumstances, hard carbonaceous coatings, represented bydiamond-like carbon films, have drawn attention as a material satisfyingthe more rigorous demands of a new era. Such hard carbonaceous coatingshave been subject to attempts at vapor phase film deposition by variousmethods, foremost among them chemical vapor deposition (CVD), but thereare various problems in the path to practical use, and the range ofapplication has been limited so far.

[0004] For example, in the most successful instances, a maximum level of3,000 kg/mm² Vickers hardness has been attained in a hard carbonaceousfilm through plasma assisted CVD methods, but a problem exists in that3,000 kg/mm² has been an actual limit. Adhesion characteristics and thesubstrate temperature during film formation also present problems to besolved with regard to conventional hard carbonaceous films resultingfrom vapor phase film deposition.

[0005] In hard carbonaceous films formed using plasma enhanced CVDprocesses, adhesion characteristics to various steel and other metallicsubstrate materials, primarily tools, are in reality poor, andimplementation into practical applications has been problematic. Thereason is that the coefficient of thermal expansion of a hardcarbonaceous film is extremely low (0.80×10⁻⁶/K). Thus, when a film isformed on a substrate material with a large coefficient, such asstainless steel 13.8×10⁻⁶/K in primary material, iron), it has not beenpossible to avoid reaching relatively high temperatures in the substratematerial during formation of the hard carbonaceous film. When thesubstrate material temperature cools down from the high temperaturereached during film-formation to ambient temperature afterfilm-formation, stress develops between the film and the substratematerial, and consequently the film peels off.

[0006] Conventional methods investigated for improving the poor adhesionof a film include forming an intermediate layer between the substratematerial and the film (a silicon compound or the like), and rougheningof the substrate material surface. However, while the first methodinitially appears to improve adhesion between the hard carbonaceous filmand the intermediate layer, in actual application in tools and the like,adhesion has still been insufficient, and the film peels off. It hasalso not been possible to obtain an intermediate layer having asufficient hardness to allow placement under a high-hardnesscarbonaceous film. The second method, like the first method, does notobtain adequate adhesion strength in actual use.

[0007] During film-formation, a substrate heating temperature of atleast 200′C or more has been required to obtain a high-hardnesscarbonaceous film. Thus, it has not been practical to apply hardcarbonaceous films to substrate materials that experience deformation ordeterioration at high temperatures, e.g., substrate materials having alow melting point or that become annealed and lose their hardness withinthis range of temperatures.

[0008] In various conventional CVD processes, gas mixtures of hydrogenand methane, or other hydrocarbon gases, have been used as the sourcefor film formation material and the incorporation of hydrogen into thecarbonaceous film was deliberate. However, as noted above, the hardnessthus obtained has been merely 3,000 kg/mm² Vickers hardness at maximum.In terms of heat-resistance, in hard carbonaceous films containinghydrogen, graphitization begins at 350′C, whereas in a film notcontaining hydrogen, graphitization does not begin unless thetemperature is 500′C or higher. The onset of graphitization causes adecline in hardness and a degradation of characteristics.

[0009] With hydrogen, the danger of ignition is also extremely high, anduse of methane gas or other such hydrocarbon gas at the same timepresents a flammability hazard.

[0010] Methods for forming a hard carbonaceous film not containinghydrogen include sputtering methods, electron beam deposition methods,and direct ion beam methods, but in these methods, hardness, wearresistance, and other such characteristics have been found to beinadequate, and for reasons including the narrow range of parameters inwhich the fllmforming process operates an article adequate for practicaluse cannot presently be obtained.

[0011] CVD methods and other such plasma processes also entail problemsin that generation of films having a uniform, large surface area hasbeen difficult. When plasma is generated adjacent to an insulating hardcarbonaceous film, once the plasma has been extinguished, growth doesnot again appear in the same location even if the plasma is regenerated,thus posing a major problem to the creation of a large, uniform surfacearea film.

SUMMARY OF THE INVENTION

[0012] Accordingly, the invention provides a method and apparatus forforming a novel carbonaceous hard film, which has a high hardnesssurpassing the hardness level previously deemed a conventional limit, issuperior in adherence to a substrate material, obviates effectsresulting from substrate temperature, and is also superior in potentialfor creation of a large surface area.

[0013] The invention provides a method and apparatus for forming acarbonaceous hard film by irradiation with gas cluster ions during orfollowing the deposition of a layer of carbonaceous material from vaporwhich may, or not, be partially ionized, wherein said method is a methodfor vapor phase film deposition of a carbonaceous hard film on asubstrate material under a vacuum-reduced pressure. The vaporizedcarbonaceous material, which may be ionized or non-ionized, is depositedonto a substrate surface. Gas clusters made up of atomic or molecularaggregate of a material, which is gaseous at ambient temperature andpressure, are ionized, accelerated and irradiated onto the surfacecontaining the layer of carbonaceous material.

[0014] The invention also provides a formation method, wherein thecarbonaceous material is one or more of a fullerene, a carbon nanotube,graphite, amorphous carbon, or a carbene not containing hydrogen. Theformation method is such that the atoms or molecules comprising the gasclusters are comprised of one or more of a rare gas, oxygen, a carbonoxide, nitrogen, a nitride, a halogen, or a halide. The Vickers hardnessof the carbonaceous hard film is more than 4,000 kg/mm² and thecoefficient of friction is 0.15 or less. In addition, the carbonaceoushard film does not contain hydrogen.

[0015] The invention provides an apparatus for forming a carbonaceoushard film on a substrate through irradiation with gas cluster ions,wherein the apparatus is equipped with a gas cluster beam generationmeans, a gas cluster ionization means, ionized gas cluster accelerationmeans, means for generating vaporized particles of carbonaceousmaterial, vaporized particles ionization means, means for accelerationof the vaporized and ionized particles of carbonaceous materials, and afilm formation unit therefore, which are disposed as necessary, andvacuum exhaust means. The gas cluster ionization and acceleration unitsand the carbonaceous material vaporized particle product, or the productof ionization and acceleration units added thereto, are directed towardsa substrate surface disposed in the film formation unit such thatindividual gas cluster ions and ionized or non-ionized carbonaceousmaterial vaporized particles are irradiated onto the substrate.

[0016] The invention also provides a carbonaceous hard film deposited ona substrate material from vapor phase, wherein the Vickers harness ismore than 4,000 kg/mm2 and the coefficient of friction is 0.15 or less,and the invention offers a carbonaceous hard film not containinghydrogen.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a schematic block diagram of a film forming apparatusthat utilizes a gas cluster ion beam in accordance with the invention;

[0018] FIGS. 2A-2D are graphs showing the change in the Raman spectrumwhen the cluster ion accelerating energy is varied;

[0019]FIG. 3 is a graph showing the change in the Vickers hardness; andFIG. 4 is a graph showing the results of measurements of the frictioncoefficient.

[0020]FIG. 4 is a graph showing the results of measurements of thefriction coefficient.

DETAILED DESCRIPTION OF THE INVENTION

[0021] A method of forming a carbonaceous hard film according to theinvention is structured according to a method characterized by vaporphase film formation by gas cluster ion beam assisted deposition.Specifically, a method of vapor-phase film formation of a carbonaceoushard film on a substrate material under a vacuum-reduced pressure isdescribed. When a vaporized carbonaceous material is deposited onto asubstrate material surface with or without ionization, a gas clustercomprising an aggregate of atoms or molecules of a material, which isgaseous at ambient temperature and pressure, is ionized, and filmformation is carried out by irradiating the gas cluster ions onto saidlayer of the carbonaceous vapor deposited on the surface of a substratematerial.

[0022] In accordance with the invention, the carbonaceous material maybe of various types excluding diamond, and examples include one or moreof a fullerene, a carbon nanotube, graphite, amorphous carbon, or acarbene not containing hydrogen. These several carbonaceous materialsare appropriate in that do not contain hydrogen other than as a possibleimpurity. Among these, fullerenes and carbon nanotubes, or homologuesthereof, have drawn recent attention from the perspective of novelcarbon material technology and are cited as ideal starting materials.

[0023] These carbonaceous materials are vaporized and deposited onto asubstrate surface either directly or after ionization. The means forvaporization may be an appropriate process such as sputtering, laserablation, ion or electron beam, or crucible heating. In the case ofionized particles, these may be accelerated and deposited on a substratesurface. The atoms or molecules comprising a gas cluster are a gas underconditions of ambient temperature and ambient pressure. Examples includeone or more of argon, helium, neon, and other rare gases; oxygen; CO₂and other carbon oxides; nitrogen; nitrides; halogens; and SF₆ and otherhalides.

[0024] The number of atoms (molecules) comprising a cluster or clusterion can be controlled by controlling the formation conditions of the gascluster, and in the method of the invention, the number thereof is notlimited but can be made, for example, 10-10,000.

[0025] The gas clusters, made up of aggregates comprising a number ofatoms (molecules) between 10-10,000 (which can be predetermined), areionized by electron bombardment, for example, and endowed with energy byacceleration to form a cluster ion beam which is then irradiated.

[0026] Conditions in the film formation of a carbonaceous hard film alsoinclude the degree of vacuum pressure reduction during film formation,the substrate material temperature during film formation, the ratio ofthe number of atoms or molecules in the vaporized particles of thecarbonaceous material or the ionized particles thereof to the number ofgas cluster ions, and the gas cluster ion accelerating voltage. Theseconditions can also be set as appropriate considering such factors asthe type of carbonaceous material or the characteristics of thecarbonaceous hard film, and the rate of film formation.

[0027] For example, a quantity of 1-10 gas cluster ions per 1-5,000molecules comprising the carbonaceous material is considered. There isalso no particular limitation with respect to the cluster ionaccelerating voltage, and the voltage is set within a range forming acarbonaceous film of desirable quality. For example, the cluster ionaccelerating voltage may be set in the range of 1 KeV-10OKeV.

[0028] Unlike the plasma CVD methods conventionally employed, there isabsolutely no need to heat the substrate in the method of the invention.Rather, a carbonaceous hard film can be formed on a substrate held atroom temperature without heating. Of course, it is also acceptable toperform heating if desired, within limits that do not interfere with themethod.

[0029] Unlike conventional plasma film forming methods, there isnegligible increase in the temperature of the substrate during theprocess of forming the film in the method herein described. For thisreason, the method can be utilized without any particular restrictionson the type of substrate employed. Moreover, the problem that has beenencountered in the conventional art, wherein there is a substantialincrease in the temperature of the substrate during film formation, doesnot occur with the present method. In addition, pre-treatments such asthe provision of an intermediate layer or roughening of the substratesurface are not required in the method of the invention.

[0030] In the method for forming a carbonaceous hard film in accordancewith the invention, if the Ar atoms which form an Ar cluster ion arepresent in the amount of 1,000 atom/ion, for example, and anaccelerating energy of 5 keV is applied to this gas cluster ion, thenthe energy per atom is the value obtained when the total energy isdivided by the number of atoms forming the cluster. In this case, thisenergy is 5 eV/atom. Accordingly, since this is an equivalently lowenergy ion beam, it is possible to form a high quality carbonaceous hardfilm in which there is minimal radiation damage such as voids.

[0031] Moreover, in the case of a gas cluster ion, a localized,instantaneous high-temperature, high-pressure state can be achieved onthe surface during multiple impacts with the surface of the substrate.Thus, it becomes possible to approach the high-temperature,high-pressure state required for diamond synthesis. As a result, acarbonaceous hard film can be obtained which has high hardness, isresistant to friction and wear, and which includes many sp³ diamondbonds which could not be achieved with the conventional methods forforming films.

[0032]FIG. 1 is a schematic block diagram of a film forming apparatus100 that utilizes a Gas cluster ion beam in accordance with theinvention. The apparatus 100 includes a gas cluster generating chamber102 and a film formation chamber 120. The gas cluster generating chamberincludes a source of gas 104, a nozzle 108, and a vacuum pump 106. Askimmer 112 separates un-clustered gas from gas clusters prior to theirentry into a differential pumping chamber 114 that includes a vacuumpump 110.

[0033] The film formation chamber includes a first ionizer 122, a firstaccelerator 124, and a deflection system 126. The chamber 120 alsoincludes a second ionizer 130 and an associated crucible 128, and asecond accelerator 132. A vacuum pump 134 serves to evacuate the chamberin which a substrate 141 is positioned by a substrate holder 140.

[0034] In an exemplary embodiment, the gas clusters are generated andradiated as follows. A high-pressure source gas 104 is expanded from thenozzle 108 of the gas cluster generating element 103 into the vacuum inthe gas cluster generating chamber 102. The energy of the source gasatoms is converted into translational motion energy, while at the sametime reducing their thermal energy by adiabatic expansion. The sourcegas atoms or molecules, which super cooled due to the loss of thermalenergy, nucleate the atoms or molecules to form gas clusters.

[0035] These neutral clusters which have formed are passed through askimmer 112 to the differential pumping chamber 114 and eventually tothe film formation chamber 120. After being ionized by ionizer 122, thegas cluster ions are accelerated by accelerator 124 towards thesubstrate 141. Deflection system 126 scans the gas cluster ion beam overthe surface of the substrate 141.

[0036] In the example shown in FIG. 1, a carbonaceous material isvaporized by heating it within the crucible 128, which is the elementfor generating the vaporized particles of the carbonaceous material.Thereafter, as needed, the vaporized particles of carbonaceous materialmay be partially ionized by ionizer 130 and the ionized particles arefurther accelerated by accelerator 132. The vaporized carbonaceousparticles, ionized or non-ionized, are deposited on the substratesurface. During film formation, the gas cluster ion beam bombards thesubstrate material. Optionally, the deposited film may also be removedfrom the device in which it was produced, to be irradiated by thecluster ion beam in a separate suitable device.

[0037] In accordance with the invention, a carbonaceous hard film can beprovided in which (1) it is a carbonaceous hard film deposited in vaporphase onto a substrate, (2) the Vickers hardness is higher than 4,000kg/mm², (3) the friction coefficient is 0.15 or less, and (4) thecarbonaceous hard film of the invention does not contain hydrogen atomsin the hard film.

[0038] The term “carbonaceous hard film” as employed herein in referenceto the invention means that the primary film component is carbon, andthat the film material is composed only of carbon, with the exception ofatoms or molecules which become unintentionally mixed in as impuritiesfrom the starting materials for vapor phase film formation or asotherwise unintended contaminants.

[0039] The carbonaceous hard film of the invention, formed in vaporphase as described above, has not been known nor concretely offeredpreviously. For example, specifically, by employing the invention, it ispossible to provide a material having a Vickers hardness of in excess of4,000 kg/mm′ and a friction coefficient of 0.15 or less. The thicknessof the carbonaceous hard film is not particularly restricted, but may bewithin the range of 1˜5 μm, for example.

[0040] Further explanation in greater detail will now be made using thefollowing examples.

[0041] Carbonaceous hard films were formed using a method in which acarbonaceous material was vapor deposited, while employing gas clusterions, on each of a silicon, SUS 304, Cr, Ni, and organic substrate.

[0042] A pure carbon fullerene (mainly C,O) was used here as thecarbonaceous material, with argon employed as the cluster source gas. Asshown in FIG. 1, by heating the crucible, the fullerene was vaporizedand vapor deposited onto the substrate. The argon cluster ions wereionized and accelerated to 1˜10 keV, and then bombarded onto the roomtemperature substrate.

[0043] By performing vapor deposition and radiation at a proportion of1-10 argon cluster ions per 1˜5,000 fullerene molecules that reach thesubstrate, it was possible to form a solid carbonaceous hard film on thevarious substrates noted above within the wide ion accelerating energyrange of 3˜9 keV. The Raman spectra of carbonaceous hard films formedfollowing radiation in which the argon cluster ion accelerating energywas varied among 3, 5, 7 and 9 keV are shown respectively in the graphsof FIGS. 2A-2D. Broad Raman spectra in the range of 1200 cm⁻¹ ˜1600 cm⁻¹ which verified the carbonaceous hard film could be obtained.

[0044] The Vickers hardness of carbonaceous hard films (film thickness:2 μm) formed following irradiation in which the argon clusteraccelerating energy was varied among 5, 7, and 9 keV are shown in thegraph of FIG. 3. The highest hardness was obtained at an argon clusterion accelerating energy of 7 keV, this hardness being approximately5,000 kg /MM2. The results of measurements of the friction coefficientare shown in the graph of FIG. 4. It was found that the frictioncoefficient was extremely small, at a value of 0.1.

[0045] In addition, a carbonaceous hard film that was sufficientlyadhered to the substrate could be obtained for all the substrateswithout carrying out a pre-treatment such as providing an intermediatelayer.

[0046] In contrast, in the CVD method that is currently employed inindustry, it is not Possible to adhere the hard carbonaceous filmwithout performing a pre-treatment to the metal substrate. Accordingly,it was understood that the film obtained using the method of theinvention could not be achieved through conventional methods for forminga hard carbonaceous film.

[0047] In addition, in the case of an organic substrate, it was alsopossible to form a carbonaceous hard film without any accompanyingchange in the character or shape of the substrate, and the substrateitself did not reach a high temperature.

[0048] As explained in detail heretofore, the invention provides aformation method in which a carbonaceous hard film can be directlydeposited onto a substrate, irrespective of whether that substrate is ametal or non-metal, without performing a pretreatment such as provisionof an intermediate layer. The carbonaceous hard film provided by theinvention may be applied to processes which require high hardness or lowfriction or both, or may be used as a high quality protective film fornon-lubricated sliding parts in the various types of machinery whichhave been put into operation in clean environments in recent years, aswell as optical lenses and filters. In addition, the carbonaceous hardfilm of the invention may also be utilized as a surface material for avariety of metal-molded industrial equipment parts, such as the variousrollers for precision molding, which must be reflective, shock resistantand resistant to chemicals, as well as have a smooth surface and be wearresistant. Accordingly, the carbonaceous hard film of the invention canbe utilized as a surface improving film for various parts in anyindustrial field. As a result of the present invention, it is possibleto provide a carbonaceous hard film that has a Vickers hardness inexcess of 4,000 kg/mm², and offers superior resistance to friction andwear, and excellent chemical stability.

[0049] Specifically, the invention provides the following effects. Thefilm can be formed at room temperature when forming the film using a gascluster ion beam. Accordingly, it was possible to form a carbonaceoushard film of sufficient adhesion on a metal substrate, such as stainlesssteel, in which there is a large difference in the coefficient ofthermal expansion between the substrate material and the carbonaceoushard film. Furthermore, it was possible to form a film onto an organicsubstrate having a low thermal deformation temperature, something thathad been problematic to achieve with the conventional technology.

[0050] In the method of the invention, there is absolutely no need toemploy the hydrogen that is used in many conventional CVD processes. Asa result, a carbonaceous hard film is formed which, as compared to thehard carbonaceous films formed using CVD processes and the like, doesnot contain hydrogen. Accordingly, none of the problems observed in hardcarbonaceous films containing hydrogen occur in the described method, sothat, as a result, it is possible to form a carbonaceous hard film thathas superior thermal stability.

[0051] By applying an electric field to a gas cluster ion beam followingacceleration, scanning thereof becomes possible by means that are wellknown in the ion beam art. By such scanning it becomes easy to increasethe area over which it is possible to obtain a film of uniform 5character and thickness, which cannot be done using a CVD method.

[0052] Accordingly, the invention enables the formation of acarbonaceous hard film having a high hardness, strong adherence to thesubstrate, a wide range of substrate selections, and structuralstability, which can be formed at room temperature and may have a largerarea, the formation of this type of film having been difficult toachieve using any of the conventional 10 methods for forming a hardcarbonaceous film.

[0053] Although the present invention has been shown and described withrespect to several preferred embodiments thereof, various changes,omissions and additions to the form and detail thereof, may be madetherein, without departing from the spirit and scope of the invention.

What is claimed is:
 1. A carbonaceous hard film vapor phase-formed on asubstrate material and having a Vickers hardness of 4,000 kg/mm² or moreand a coefficient of friction of 0.15 or less.
 2. A carbonaceous hardfilm of claim 1 wherein said film does not contain hydrogen.